This invention relates to the control of weed growth in lawns and gardens and, more particularly, to chemical control of weed growth.
Weed control by the application of chemicals in lawns and gardens has been widely used, and has been found to be the most effective and convenient method for controlling weeds. In such method, chemical compounds called herbicides such as 2,4-dichlorophenoxyacetic acid are deposited by spraying onto the weeds. The herbicides will cause the weeds to defoliate and eventually to die, yet the herbicides are not harmful to grass.
Chemical herbicides are commonly provided to the user in the form of concentrated aqueous solutions. The user must dilute the aqueous solution into a workable solution of a predetermined concentration, and the dilute solution is sprayed over the entire lawn or in selected areas where weeds are growing actively. However, the herbicidal solution thus prepared cannot be applied to the lawn in rainy weather since it will either be highly diluted by the rain or be washed away thereby. Heavy dew will also weaken the effectiveness of the herbicidal solution. Also, it cannot be used in windy conditions even when the wind is moderate, because the spray and fume of the herbicidal solution can be easily carried away by the wind. The spray and fume of the herbicides carried by the wind are harmful to human as well as to other ornamental plants located in the neighbourhood, thus this presents a large problem to the effective application of such herbicides.
In order to avoid breathing in the fume and vapour of the herbicide, the user may drag the applicator behind him so that the harmful fume and vapour are blown away from him. This common practice also enables the user to avoid walking over the treated area so that the herbicidal solution of the applied area cannot cause contamination to his clothing. However, in doing so the user would not have a clear view of the area being treated and the applicator is not under his full control.
Furthermore, the herbicidal solution must be prepared carefully according to the recommended concentration and applied to the lawn evenly in a correct quantity. An excess amount of herbicides used will cause the grass to wilt or brown; a condition which is referred to as "burning" of the grass, making the lawn very unsightly and resulting in unhealthy grass growth. Also, herbicides are poisonous, and it is thus hazardous for the user to handle the concentrated aqueous solution of the herbicides in preparing the solution for use.
Attempts have been made to alleviate the problems of using liquid herbicides by admixing the herbicides with a solid base to form a solid herbicidal composition which can be applied by rubbing it on the weed plants. It does not require the user to prepare the solution and it can be used in a windy condition without the danger of spreading the herbicides to neighbouring trees and ornamental plants in herbaceous borders. However, known solid herbicidal compositions suffer the main drawback that they have a low melting point and they are readily melted by the solar heat after application to weeds such that they would run off into the soil or be diluted or washed away by rain or dew as in using liquid herbicidal compositions. Moreover, known solid herbicidal compositions when melted by the solar heat release the herbicides at an excessive rate to a point causing damage to the grass in the treated areas. This is mainly due to the fact that natural waxes have been used as the base carrier which have a low melting point. Also such solid herbicidal compositions often become very soft and tacky in summertime and the herbicides can be exuded from the composition due to the ambient heat. The exuded herbicides are then lost by volatilization into vapour which is harmful and may also cause contamination to other material placed nearby.
In spite of the low melting point, known solid herbicidal compositions have a low adhesiveness and they must be rubbed with a considerable pressing force so as to apply a satisfactory amount of the compositions on weed plants, and they are not adherent to wet weed plants.
Moreover, natural waxes break down readily in exposure to solar heat and atmosphere. Thus, they remain in the weed plants for a relatively short period without permitting the herbicides to act effectively on the weed plants.